refactor(cli): add async version of resolve_addr function

[magurotuna]

While I'm looking into #7824, I found to_socket_addrs, which is a blocking API, was called in resolve_addr function.
So this commit adds a new function that is an asynchronous version of resolve_addr using tokio::net::lookup_host.
And accordingly, renames the synchronous version to resolve_addr_sync.
This allows async ops to resolve hosts with non-blocking.

[ry]

Nice work. Thanks!

It would be cool to expose these as standalone ops!

I am concerned that the asynchronous version does not go through the system's getaddrinfo() and potentially ignores things like /etc/hosts. Does tokio::net::lookup_host call getaddrinfo() in a thread pool (with spawn_blocking) or is it using a separate asynchronous DNS stack?

[magurotuna]

@ry

It would be cool to expose these as standalone ops!

Sure, I'll do that.

I am concerned that the asynchronous version does not go through the system's getaddrinfo() and potentially ignores things like /etc/hosts. Does tokio::net::lookup_host call getaddrinfo() in a thread pool (with spawn_blocking) or is it using a separate asynchronous DNS stack?

Good point. Looking at tokio's implementation, it eventually calls std::net::ToSocketAddrs with spawn_blocking.
Refs:

• the lastet version(0.3.6): https://docs.rs/tokio/0.3.6/src/tokio/net/addr.rs.html#207
• the version Deno is currently using(0.2.22): https://docs.rs/tokio/0.2.22/src/tokio/net/addr.rs.html#199

[ry]

LGTM - thanks!